Fair Value - Quantitative Disclosure for Assets Classified as Level 3 (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Balance at December 31, 2013	$ 7,513
Gains included in net income	85
Gains included in comprehensive income	47
Investments and capital calls	3,080
Distributions received	(195)
Balance at December 31, 2014	10,530
Common Stock at Fair Value [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Gains included in comprehensive income	47
Investments and capital calls	900
Balance at December 31, 2014	947
Net Asset Value [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Balance at December 31, 2013	3,314
Gains included in net income	81
Investments and capital calls	2,180
Distributions received	(195)
Balance at December 31, 2014	5,380
Equity Method [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Balance at December 31, 2013	4,199
Gains included in net income	4
Balance at December 31, 2014	$ 4,203